//! 集群管理模块
//! 
//! 提供分布式数据库集群的管理功能，包括节点发现、负载均衡、
//! 数据分片、故障转移等核心功能。

use crate::{Error, Result};
use std::collections::HashMap;
use std::sync::Arc;
use parking_lot::RwLock;
use std::net::SocketAddr;
use tokio::sync::mpsc;
use serde::{Serialize, Deserialize};

pub mod node;
pub mod consensus;
pub mod replication;
pub mod load_balancer;
pub mod cluster_engine;
pub mod cluster_engine_simple;

/// 集群管理器
#[derive(Debug)]
pub struct ClusterManager {
    /// 集群配置
    config: ClusterConfig,
    /// 节点管理器
    node_manager: Arc<RwLock<node::NodeManager>>,
    /// 共识算法
    consensus: Arc<RwLock<consensus::ConsensusEngine>>,
    /// 复制管理器
    replication: Arc<RwLock<replication::ReplicationManager>>,
    /// 负载均衡器
    load_balancer: Arc<RwLock<load_balancer::LoadBalancer>>,
    /// 集群状态
    cluster_state: Arc<RwLock<ClusterState>>,
}

/// 集群配置
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ClusterConfig {
    /// 集群名称
    pub cluster_name: String,
    /// 当前节点ID
    pub node_id: String,
    /// 监听地址
    pub listen_addr: SocketAddr,
    /// 种子节点列表
    pub seed_nodes: Vec<SocketAddr>,
    /// 复制因子
    pub replication_factor: usize,
    /// 心跳间隔（毫秒）
    pub heartbeat_interval_ms: u64,
    /// 选举超时（毫秒）
    pub election_timeout_ms: u64,
}

/// 集群状态
#[derive(Debug, Clone)]
pub struct ClusterState {
    /// 集群ID
    pub cluster_id: String,
    /// 当前任期
    pub current_term: u64,
    /// 领导者节点ID
    pub leader_id: Option<String>,
    /// 活跃节点数
    pub active_nodes: usize,
    /// 集群健康状态
    pub health_status: ClusterHealth,
}

/// 集群健康状态
#[derive(Debug, Clone, PartialEq)]
pub enum ClusterHealth {
    /// 健康
    Healthy,
    /// 警告
    Warning,
    /// 不健康
    Unhealthy,
    /// 分裂
    Split,
}

/// 集群事件
#[derive(Debug, Clone)]
pub enum ClusterEvent {
    /// 节点加入
    NodeJoined(String),
    /// 节点离开
    NodeLeft(String),
    /// 领导者变更
    LeaderChanged(Option<String>),
    /// 分片重新分配
    ShardRebalanced,
    /// 故障转移
    Failover(String),
}

impl ClusterManager {
    /// 创建新的集群管理器
    pub fn new(config: ClusterConfig) -> Result<Self> {
        let node_manager = Arc::new(RwLock::new(node::NodeManager::new(config.clone())?));
        let consensus = Arc::new(RwLock::new(consensus::ConsensusEngine::new(config.clone())?));
        let replication = Arc::new(RwLock::new(replication::ReplicationManager::new(config.clone())?));
        let load_balancer = Arc::new(RwLock::new(load_balancer::LoadBalancer::new(config.clone())?));
        
        let cluster_state = Arc::new(RwLock::new(ClusterState {
            cluster_id: format!("cluster_{}", config.cluster_name),
            current_term: 0,
            leader_id: None,
            active_nodes: 0,
            health_status: ClusterHealth::Healthy,
        }));
        
        Ok(Self {
            config,
            node_manager,
            consensus,
            replication,
            load_balancer,
            cluster_state,
        })
    }
    
    /// 启动集群管理器
    pub async fn start(&self) -> Result<()> {
        tracing::info!("启动集群管理器: {}", self.config.cluster_name);
        
        // 启动节点管理器
        self.node_manager.write().start().await?;
        
        // 启动共识引擎
        self.consensus.write().start().await?;
        
        // 启动复制管理器
        self.replication.write().start().await?;
        
        // 启动负载均衡器
        self.load_balancer.write().start().await?;
        
        tracing::info!("集群管理器启动完成");
        Ok(())
    }
    
    /// 停止集群管理器
    pub async fn stop(&self) -> Result<()> {
        tracing::info!("停止集群管理器");
        
        // 停止各个组件
        self.load_balancer.write().stop().await?;
        self.replication.write().stop().await?;
        self.consensus.write().stop().await?;
        self.node_manager.write().stop().await?;
        
        tracing::info!("集群管理器已停止");
        Ok(())
    }
    
    /// 加入集群
    pub async fn join_cluster(&self) -> Result<()> {
        tracing::info!("加入集群: {}", self.config.cluster_name);
        
        // 连接种子节点
        for seed_addr in &self.config.seed_nodes {
            match self.connect_to_seed(*seed_addr).await {
                Ok(_) => {
                    tracing::info!("成功连接到种子节点: {}", seed_addr);
                    break;
                }
                Err(e) => {
                    tracing::warn!("连接种子节点失败 {}: {}", seed_addr, e);
                }
            }
        }
        
        Ok(())
    }
    
    /// 连接到种子节点
    async fn connect_to_seed(&self, addr: SocketAddr) -> Result<()> {
        // 简化实现：实际需要建立网络连接
        tracing::debug!("连接到种子节点: {}", addr);
        Ok(())
    }
    
    /// 获取集群状态
    pub fn get_cluster_state(&self) -> ClusterState {
        self.cluster_state.read().clone()
    }
    
    /// 获取集群配置
    pub fn get_config(&self) -> &ClusterConfig {
        &self.config
    }
    
    /// 处理集群事件
    pub async fn handle_event(&self, event: ClusterEvent) -> Result<()> {
        tracing::debug!("处理集群事件: {:?}", event);
        
        match event {
            ClusterEvent::NodeJoined(node_id) => {
                self.on_node_joined(&node_id).await?;
            }
            ClusterEvent::NodeLeft(node_id) => {
                self.on_node_left(&node_id).await?;
            }
            ClusterEvent::LeaderChanged(leader_id) => {
                self.on_leader_changed(leader_id).await?;
            }
            ClusterEvent::ShardRebalanced => {
                self.on_shard_rebalanced().await?;
            }
            ClusterEvent::Failover(node_id) => {
                self.on_failover(&node_id).await?;
            }
        }
        
        Ok(())
    }
    
    /// 处理节点加入事件
    async fn on_node_joined(&self, node_id: &str) -> Result<()> {
        tracing::info!("节点加入集群: {}", node_id);
        
        // 更新集群状态
        {
            let mut state = self.cluster_state.write();
            state.active_nodes += 1;
        }
        
        // 触发负载重新平衡
        self.load_balancer.write().rebalance().await?;
        
        Ok(())
    }
    
    /// 处理节点离开事件
    async fn on_node_left(&self, node_id: &str) -> Result<()> {
        tracing::info!("节点离开集群: {}", node_id);
        
        // 更新集群状态
        {
            let mut state = self.cluster_state.write();
            if state.active_nodes > 0 {
                state.active_nodes -= 1;
            }
        }
        
        // 检查是否需要故障转移
        if Some(node_id.to_string()) == self.cluster_state.read().leader_id {
            self.trigger_leader_election().await?;
        }
        
        Ok(())
    }
    
    /// 处理领导者变更事件
    async fn on_leader_changed(&self, leader_id: Option<String>) -> Result<()> {
        tracing::info!("领导者变更: {:?}", leader_id);
        
        // 更新集群状态
        {
            let mut state = self.cluster_state.write();
            state.leader_id = leader_id;
        }
        
        Ok(())
    }
    
    /// 处理分片重新平衡事件
    async fn on_shard_rebalanced(&self) -> Result<()> {
        tracing::info!("分片重新平衡完成");
        Ok(())
    }
    
    /// 处理故障转移事件
    async fn on_failover(&self, node_id: &str) -> Result<()> {
        tracing::info!("执行故障转移: {}", node_id);
        
        // 启动故障转移流程
        self.replication.write().handle_failover(node_id).await?;
        
        Ok(())
    }
    
    /// 触发领导者选举
    async fn trigger_leader_election(&self) -> Result<()> {
        tracing::info!("触发领导者选举");
        self.consensus.write().start_election().await
    }
    
    /// 检查集群健康状态
    pub async fn check_cluster_health(&self) -> ClusterHealth {
        let state = self.cluster_state.read();
        let total_nodes = self.config.seed_nodes.len() + 1; // 包括当前节点

        // 如果只有一个节点（当前节点），认为是健康的
        if total_nodes == 1 {
            return ClusterHealth::Healthy;
        }

        let health_ratio = state.active_nodes as f64 / total_nodes as f64;

        if health_ratio >= 0.8 {
            ClusterHealth::Healthy
        } else if health_ratio >= 0.6 {
            ClusterHealth::Warning
        } else if health_ratio >= 0.3 {
            ClusterHealth::Unhealthy
        } else {
            ClusterHealth::Split
        }
    }
}

impl Default for ClusterConfig {
    fn default() -> Self {
        Self {
            cluster_name: "cdb-cluster".to_string(),
            node_id: "node-1".to_string(),
            listen_addr: "127.0.0.1:7000".parse().unwrap(),
            seed_nodes: vec![],
            replication_factor: 3,
            heartbeat_interval_ms: 1000,
            election_timeout_ms: 5000,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    
    #[tokio::test]
    async fn test_cluster_manager_creation() {
        let config = ClusterConfig::default();
        let cluster_manager = ClusterManager::new(config).unwrap();
        
        let state = cluster_manager.get_cluster_state();
        assert_eq!(state.cluster_id, "cluster_cdb-cluster");
        assert_eq!(state.current_term, 0);
        assert_eq!(state.leader_id, None);
        assert_eq!(state.active_nodes, 0);
        assert_eq!(state.health_status, ClusterHealth::Healthy);
    }
    
    #[tokio::test]
    async fn test_cluster_health_check() {
        let config = ClusterConfig::default();
        let cluster_manager = ClusterManager::new(config).unwrap();
        
        let health = cluster_manager.check_cluster_health().await;
        assert_eq!(health, ClusterHealth::Healthy);
    }
    
    #[tokio::test]
    async fn test_cluster_events() {
        let config = ClusterConfig::default();
        let cluster_manager = ClusterManager::new(config).unwrap();
        
        // 测试节点加入事件
        cluster_manager.handle_event(ClusterEvent::NodeJoined("node-2".to_string())).await.unwrap();
        let state = cluster_manager.get_cluster_state();
        assert_eq!(state.active_nodes, 1);
        
        // 测试节点离开事件
        cluster_manager.handle_event(ClusterEvent::NodeLeft("node-2".to_string())).await.unwrap();
        let state = cluster_manager.get_cluster_state();
        assert_eq!(state.active_nodes, 0);
    }
}
